Subsurface drain systems are particularly vulnerable to infiltration into them of unwanted fluids. For example, a sanitary waste system comprises plumbing collection systems in buildings where waste is generated, an external sewer collection system and a treatment plant. The plumbing and sewer systems are typically designed to operate at half-full (or a lot less because of minimum pipe sizes). However, the treatment facility may be designed to operate at up to about ninety percent (90%) of its capacity and enlarging such capacity is difficult and very expensive to do. Moreover, operating costs increase with fluid quantities and treatment methods are similar whether the waste is raw or swelled with storm water which has infiltrated the plumbing and sewer systems. During heavy storms, some older treatment plants may get up to twice the amount of waste seen during more normal periods.
The collection systems experience infiltration for many reasons and from various sources. For example, the collection systems operate by gravity so access for air to or from such drains is provided through venting devices. Also, drain pipes in the systems are vulnerable to clogging by waste and debris so other access for inspection and cleaning is provided through devices such as lamphole, manhole and smaller, cleanout devices. Unfortunately, many venting and other access devices are installed at or below surfaces which carry runoff water during storm periods and such runoff gets into the drains. Moreover, the amount of such runoff is increasing to unexpected levels because of dense proliferation of buildings, shopping centers and substantially impervious paved surfaces. Surface-located, access devices often take on and pass to the subsurface drains too much water to be efficiently handled at a treatment plant so efforts are often made to seal such devices from unwanted fluids such as runoff water.
Prior art structures for sealing accessholes to subsurface drains were installed primarily in popular, cylindrical style, sewer manholes having circular frames and covers. Such covers could not be dropped through, but were often spinned in, the frames by manipulation during closing, so sealing structures were downwardly depressed to avoid collision and damage by such spinning of covers. Many features were included in an effort to close tightly against the frames and to completely seal all fluids from passing to and from the sewers. Such fluids primarily included errant storm water passing into a sanitary sewer but other fluids could not be ignored. For example, gas such as air is moved into and out of a sewer by short term vacuum and pressure conditions caused by flowing waste and temperature conditions. Also, garages and similar service buildings sometimes contribute gases which form in and must be relieved from a sewer to avoid explosions.
In some fully sealing, prior art structures, gases are bled into and off of a sewer by spring-loaded valves which require a measurable pressure differential over a respective valve between a drain and a surface to function. Such valves are costly to make, costly to repair or replace and a problem to keep operating because of dirt which tends to enter and cling to valve mechanisms. Two valves are typically installed in walls above the bottom of a structure to avoid dirt to handle vacuum and pressure separately, or so one may function when the other is inoperable. After a first storm, there is permanently trapped in such a seal, a sizable quantity of water wherein foul-smelling and disease propagating organisms may breed.
Accordingly, it is desirable to develop new and improved expedients for sealing a device having an accesshole to a subsurface drain. Such expedients should be simple in design, inexpensive to make and install and easy to maintain. Traditional teaching leads to fully sealed structures which require valves needing differential pressures thereover to operate and such seals are complex, costly and difficult to maintain. Such teaching needs reviewing to develop expedients which are simple and sanitary and which can readily be extended to housetrap vents and cleanout devices in plumbing systems as well as street manholes.